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PubMed1997

Simulated hibernation of sea turtles in the laboratory: I. Feeding, breathing frequency, blood pH, and blood gases.

Captive immature green (Chelonia mydas) and Kemp's ridley (Lepidochelys kempi) sea turtles were examined to determine if a hibernation-like state could be induced under controlled conditions. Both species demonstrated that they are able to acclimate to cold temperatures behaviorally. However, the two species appeared to respond differently to decreasing temperature. Whereas the green turtles tolerated the onset of cold water temperatures by reducing swimming activity, the ridleys became very agitated and active as they were exposed to temperatures below 20 degrees C. Nevertheless, both species displayed semi-dormant behavior at temperatures below 15 degrees C, coming to the surface to breathe periodically at intervals of up to three hours. At low temperatures, venous blood pO2 and pCO2 decreased, whereas venous blood pH increased. Feeding also decreased as either species was exposed to cold temperature: greens (at 15 degrees C) and ridleys (at 20 degrees C) decreased food consumption to 50% of control levels, and ceased feeding below 15 degrees C. Thus, these species tolerated temperature drops and the associated hypophagia. They did not exhibit cold-stunning behavior, as has been observed in wild sea turtles exposed to rapid temperature drops, or prolonged periods of hibernation-like dormancy, as has been proposed for wild sea turtles during cold winter months.

Animals↗
PubMed1989

Temperature and voltage dependence of sodium channel blocking and unblocking by O-demethyl encainide in isolated guinea pig myocytes.

O-demethyl encainide (ODE) is a metabolite of encainide with potent antiarrhythmic effects. We studied block of sodium channels by ODE in isolated guinea pig ventricular myocytes, using both direct measurement of whole cell sodium current and Vmax. Specifically, we examined whether block by ODE was use-dependent, whether ODE blocked activated or inactivated channels, and whether ODE's effect depended on membrane potential. At cold temperatures (15-20 degrees C), ODE was a potent blocker of activated cardiac sodium channels, with little or no effect on inactivated channels. At these temperatures, there was no detectable diastolic recovery from block. Repeated depolarizations produced use-dependent unblocking, which increased as the holding potential was made more negative. At warmer temperatures, use-dependent unblocking was increased, the availability curve of sodium channels for use-dependent unblocking was less shifted toward negative potentials, and diastolic recovery from block became detectable, albeit slow (tau approximately 25 s). Our findings demonstrate that electrophysiologic effects of agents such as ODE may be both quantitatively and qualitatively different at cold temperatures than at normal body temperature. One should be cautious about extrapolating electrophysiologic data obtained at cold temperatures to clinical situations.

Anilides↗
PubMed1991

Thermal stress modulates temporal patterns of responding on a multiple DRL-FR schedule.

To investigate temporal changes in behavior induced by moderate cold temperatures, rats performing on a multiple differential-reinforcement-of-low-rate (DRL) fixed-ratio (FR) schedule were exposed to ambient temperatures of 2, 8, 16, and 24 degrees C. DRL response rates markedly increased with decreasing cold temperatures, while FR response rates remained unchanged. In addition, as ambient temperatures decreased, the interresponse time (IRT) distribution of DRL responses shifted toward shorter times and short IRT bursts increased. Compared with cold effects, exposure to 38 degrees C heat induced decreases in both DRL and FR response rates which were associated with increases in long IRTs. Decreases in reinforcement frequency was associated only with the DRL schedule in cold, and with both DRL and FR schedules during heat exposures. The distinct effects of cold and heat on both DRL and FR responding suggest that the increases in DRL response rates and shifts in IRT distribution are unique to cold, and are not due to general effects of nonspecific thermal change in the ambient environment.

Animals↗
PubMed1995

Circannual changes in thyroid hormone physiology: the role of cold environmental temperatures.

Hypothyroid subjects given a constant dose of thyroxine (T4) show both an increase in serum thyrotrophin (TSH) of approximately 50% and a decline of serum T4 by approximately 15% during the winter months. Euthyroid subjects who are older than 41 years of age show an increase of approximately 30% in serum TSH during the winter months without a change in T4. Young euthyroid subjects, between the ages of 19 and 41 years, show neither a circannual pattern of TSH nor T4 but have an increase in triiodothyronine (T3) plasma clearance rate and production rate of approximately 30% during the winter seasons. Additionally, young subjects living for greater than 5 months in Antarctica show a doubling in T3 plasma clearance rate and production rate, as well as elevations of approximately 30-50% in TSH and small declines in T4. Repeated exposure to cold air has recently been reported to induce declines in serum T3, and T4 and increases in T3 clearance and production rate, thus linking a possible physiological stimulus to these seasonal observations. This collection of studies from several laboratories supports the concept that T3 kinetic changes have a seasonal dependence and that cold exposure provides one possible mechanism. As the subjects age, have a fixed thyroid hormone dosage for hypothyroxinemia, or spend an extended number of months in polar conditions, a reflex TSH rise occurs. This rise in TSH signals a hypothalamic-pituitary hypothyroxinemia whose clinical significance is unknown.

Adult↗
PubMed2005

Changes in sleep on chronic exposure to warm and cold ambient temperatures.

Alterations in sleep induced by chronic exposure to mild changes in ambient temperature (Ta) were studied in male Wistar rats with chronically implanted electrodes for recording electrooculogram (EOG), electroencephalogram (EEG) and electromyogram (EMG), and a thermocouple to record the brain temperature (Tbr). Changes in sleep-wakefulness (S-W) and Tbr on exposure to warm (30+/-1 degrees C) and cold (18+/-1 degrees C) Ta for 4 weeks were studied in two groups of five rats each. Chronic heat exposure produced a persistent increase in sleep, primarily due to an increase in the durations of sleep episodes. A disproportionate increase in sleep during the dark period resulted in reduced circadian variation. The paradoxical sleep (PS)/total sleep time (TST) ratio also remained increased, during heat exposure. On chronic cold exposure, the sleep was decreased initially, but it recovered after 3 weeks, due to an increase in the frequency of slow wave sleep (SWS) episodes. The Tbr was not altered on exposure to warm Ta, but it remained high throughout the 4 weeks of cold exposure. The increase in the amount of sleep, especially the PS with enhanced ambient temperature, may be considered as an adaptation to thermal load aimed at energy conservation. Though the increased wakefulness is suggested to enable the organism to optimize thermoregulation during acute cold stress, thermoregulation itself may be readjusted to ensure homeostatic restoration of sleep during chronic cold exposure.

Animals↗
PubMed1999

Effects of temperature and photoperiod on thermogenesis in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus).

We examined the effects of temperature and photoperiod on metabolic thermogenesis and the thermogenic characteristics of brown adipose tissue in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus), the dominant species of small mammals in the alpine meadow ecosystems on the Qinghai-Tibetan Plateau. Pikas and voles were acclimated in the following groups: (1) Long day-warm temperature (16L:8D, 23 degrees C) (2) Long day-cold temperature (16L:8D, 5 degrees C), (3) short day-warm temperature (8L:16D, 23 degrees C), and (4) short day-cold temperature (8L:16D, 5 degrees C). Both temperature and photoperiod were important environmental cues for changes in thermogenesis for both species. Low temperature and short photoperiod induced increases in metabolic rate, nonshivering thermogenesis (NST), mitochondrial protein contents of brown adipose tissue, and cytochrome C oxidase activity of brown adipose tissue mitochondria in both species. Plateau pikas were more sensitive to cold (79% of the total NST response) than to short photoperiod (21%), while root voles were more sensitive to short photoperiod (60% of the total NST response) than to cold (40%), although cold clearly enhanced thermogenesis. Their thermogenic characteristics correlated with their preferred habitats: plateau pikas are found mainly in more exposed microhabitats in open sunny meadow, while root voles live in more sheltered microhabitats in relatively closed shrub. Our results also showed that temperature and photoperiod combined induce thermogenic adjustments in both species in seasonal acclimatization in their alpine meadow macrohabitat.

Acclimatization↗
PubMed2004

Pulp responses to precise thermal stimuli in dentin-sensitive teeth.

The purpose of this study was to determine whether pulpal responses to cold temperatures applied to enamel, using a method that precisely controls the intensity of the cold stimulus or measures the response time, could distinguish dentin-sensitive teeth from nonsensitive teeth. Eighteen human subjects were stimulated with cold temperatures decreasing in 5 degree C intervals (and with tetrafluoroethane) on exposed root and enamel of a dentin-sensitive tooth and enamel of a contralateral nonsensitive tooth. Pain threshold, intensity of pain, time to pain onset, and duration of pain at baseline, 4 h, 8 h, and 1 week were measured. Responses to enamel stimulation of sensitive teeth compared with the nonsensitive teeth usually were highly correlated and not significantly different. The exception was a longer duration of pain in the dentin-sensitive teeth (4.62 +/- 0.47 s) compared with nonsensitive teeth (2.92 +/- 0.49 s; p = 0.016) after enamel stimulation with tetrafluoroethane. Longitudinal studies are necessary to determine whether these slight increases in pain duration indicate an increased probability of pulpal degeneration or need for dentin protection.

Cold Temperature↗
PubMed1999

Thyroid development in relation to the development of endothermy in the red-winged blackbird (Agelaius phoeniceus).

We investigated the development of thyroid function during the transition to endothermy in red-winged blackbirds (Agelaius phoeniceus). Thermoregulatory capabilities of blackbirds improve markedly over their relatively short nestling period (10-12 days), with the most striking improvements occurring between days 6 and 8. We hypothesized that the development of endothermy in these birds is dependent in part on the development of thyroid function. We assessed thyroid development by measuring changes in thyroid gland histology and plasma concentrations of thyroxine (T4) and triiodothyronine (T3) during the nestling period. To gain insight into the role of thyroid maturation in the context of thermoregulation, we compared plasma thyroid hormone profiles in nestlings exposed to cold temperatures to those maintained at thermoneutral temperatures. The overall size of the thyroid (as cross-sectional area) increased during nestling development, with the fastest growth occurring just before the development of endothermy. By day 8, it reached the size typical of that in adults. Follicular cell height of the thyroid glands increased in nestlings up to day 6 and then decreased for the rest of the nestling period. The mean area of individual follicles increased up to day 8 of nestling life and then decreased. Individual nestlings were capable of strong endothermic responses at 7 to 8 days of age and had significantly decreased plasma T4 concentrations following cold exposure, suggesting increased T4 to T3 deiodination to maintain the plasma concentrations of the more metabolically active T3. The patterns of plasma T4 and T3 during nestling development were consistent with those of nestlings of other altricial species of birds that have been studied. Overall, the patterns of thyroid development observed were consistent with the hypothesis that the functional development of the thyroid is critical to the development of endothermic capabilities and that thyroid hormones play a role in endothermic responses to cold temperatures.

Animals↗
PubMed1976

Chloroplastic proteins of wheat and rye grown at warm and cold-hardening temperatures.

Soluble proteins and membrane polypeptides were separated from chloroplasts isolated intact from a cultivar each of spring wheat, winter wheat, and more freeze-resistant rye, and changes in them associated with cold hardening were detected by means of polyacrylamide gel electrophoresis. No drastic changes in chloroplast membrane polypeptides occurred during growth at low temperatures in the three cultivars. However, subtle changes were evident in the soluble chloroplast protein fraction. In this fraction at least one varietal difference was discernable, yet all cultivars produced a new protein band of lowest mobility during growth at low temperatures. After the preparations were fractionated by Sephadex G-50 all unhardened plant material displayed two peaks in the region of the fraction I protein band, whereas all cold-hardening material displayed one peak. A different band of soluble protein was present only after cold hardening in Kharkov whear and Puma rye, and was not present in extracts from the cold-grown spring wheat.

Chloroplasts↗
PubMed1984

Effect of a cold ambient temperature on the rat's food hoarding behavior.

In a first experiment, the amount of food hoarded in three hour sessions (HB) by eight food deprived rats, was measured at three ambient temperatures: 30, 17.5 and 5 degrees C. At the three temperatures, the mass of food pellets hoarded by the rats was linearly related to the rats' body weight (BW) with a negative slope. The slope of the regression lines was significantly higher at 5 and 17.5 degrees C than at 30 degrees C. In a second experiment, BW and HB of ten non-deprived rats were measured every day, first at 30, then at 10 degrees C, then at 30 degrees C again (70 days). In the cold environment, HB immediately increased without BW loss. This effect was immediately reversible by the adjunction of an insulating styrofoam mattress. HB of non deprived rats in the cold was therefore more a thermoregulatory behavior than an alimentary response. In a third experiment, ad lib fed or deprived rats could hoard either food pellets or styrofoam lumps at 30 degrees C or at 5 degrees C. In the cold environment, when non-deprived, the rats hoarded styrofoam rather than food. However, as soon as they were food deprived, they reversed their choice and hoarded food rather than styrofoam. It is concluded that food can be hoarded as a thermal insulator in a cold environment but HB is mainly an alimentary response increased by a cold stress.

Animals↗
PubMed1994

Mechanisms of cold intolerance in patients with angina.

OBJECTIVES: Patients with angina often report that symptoms are worse in cold weather. This study was designed to determine differences between cold-tolerant and cold-intolerant patients in the hemodynamic and ischemic response to exercise at cold temperatures and to assess the role of catecholamines and baroreceptor function. BACKGROUND: Studies have suggested that the heart rate response may differ at cold temperatures, but the mechanism and role of this variation have not been examined. METHODS: Seven cold-intolerant and seven cold-tolerant patients with angina underwent exercise treadmill testing at 6 and 25 degrees C with measurement of catecholamines. Baroreceptor function was assessed by the decrease in systolic blood pressure after patients stood up from the supine position. RESULTS: Norepinephrine levels increased by 139% in the cold environment, but there were no differences between cold-intolerant and cold-tolerant patients. Consequently, blood pressure was higher in the cold environment in all patients, but the heart rate response was similar. However, cold-intolerant patients had a steeper heart rate response in the cold and developed ischemia (mean [+/- SEM] 201 +/- 58 vs. 242 +/- 50 s, p = 0.05) and angina (348 +/- 87 vs. 449 +/- 60 s, p = 0.04) earlier in the cold environment, a difference not seen in the cold-tolerant patients. Baroreceptor function was impaired in cold-intolerant patients (decrease in systolic blood pressure after patients stood up from the supine position 19 +/- 7 vs. 0 +/- 4 mm Hg, p = 0.04). CONCLUSIONS: Exposure to cold causes an increase in blood pressure with an associated increase in myocardial oxygen demand in all patients. In cold-tolerant patients, this increase may be offset by a reduction in heart rate if baroreceptor function is normal. If baroreceptor function is abnormal, heart rate may not decrease in response to a cold-induced increase in blood pressure. This mechanism may account for some of the variability in tolerance to cold exposure that affects patients with exertional angina.

Angina Pectoris↗
PubMed2004

Cold weather and GP consultations for respiratory conditions by elderly people in 16 locations in the UK.

BACKGROUND: Cold weather is associated with increases in mortality and demands on hospital services in the UK, particularly by the elderly. Less is known about the relationship with patterns of consultation in primary care. We wished to determine the magnitude and consistency of associations between cold temperature and consultations for respiratory conditions in primary care settings at different sites in the UK. METHODS: Time series analysis of any short-term effects of temperature on daily general practitioner (GP) consultations made by elderly people (65+ years) for lower and upper respiratory tract infections (LRTI, URTI) over a 10-year period, 1992--2001. Practices were situated in 16 urban locations across the UK where a Met Office monitoring station was in operation. RESULTS: An association between low temperatures and an increase in LRTI consultations was observed in all 16 locations studied. The biggest increase was estimated for the Norwich practices for which a 19.0% increase in LRTI consultations (95% CI 13.6, 24.7) was associated with every 1 degrees C drop in mean temperature below 5 degrees C observed 0-20 days before the day of consultation. Slightly weaker relationships were observed in the case of URTI consultations. A north/south gradient, with larger temperature effects in the north, was in evidence for both LRTI and URTI consultations. CONCLUSIONS: An effect that was consistent and generally strongest in populations in the north was observed between cold temperature and respiratory consultations. Better understanding of the mechanisms by which cold weather is associated with increases in consultations for respiratory infections could lead to improved strategies for prevention and reduced burdens for health services.

Aged↗
PubMed1992

Temperature-dependent effects of maternal separation on growth, activity, and amphetamine sensitivity in the rat.

This study was conducted to examine the effects of an early stressor, maternal separation, on development, arousal, and sensitivity to amphetamine in the rat. Rat pups were maternally separated at nest temperature (WARM), room temperature (COLD), or nest temperature with agitation (AGIT) for 6 hr each day from 2 to 15 days of age. A control group (CONT) remained with the mother in the nest during this time. COLD subjects were developmentally delayed and had lower body and brain weights than the other three groups into adulthood. WARM and AGIT subjects (both maternally separated at nest temperature) had significant growth delays compared to CONT, but grew more quickly than COLD subjects. COLD subjects were less active than the other maternally separated groups, and WARM and AGIT groups were more active. Activity did not differ at 28 or 75 days of age. However, adult WARM subjects were less sensitive and COLD subjects were more sensitive to amphetamine as measured by locomotor activity than CONT and AGIT subjects, who did not differ from each other. The relationship between early stress, changes in dopaminergic systems, and altered drug responsiveness are discussed in terms of the implications for the etiology of drug abuse.

Amphetamine↗
PubMed1985

Circadian and seasonal variations of lipogenesis in the Gulf killifish, Fundulus grandis.

Lipogenesis was measured in male Gulf killifish at three seasons under different environmental conditions. Cold temperature is stimulatory for lipogenesis in the fall and spring, but warm temperature is more stimulatory during the summer. The highest rate of lipogenesis occurs during the spring. However, total body fat content is relatively low at that time, which suggests that lipids are being actively mobilized as well. A high rate of lipogenesis also occurs at a cold temperature (20 degrees C) during the fall, and more lipids are stored at that time of year, as evidenced by higher liver and body fat stores. Both lipogenesis and total body fat content are at a minimum during the summer. These results indicate that high levels of lipid synthesis do not necessarily result in higher body fat content, as the latter is the product of both lipid synthesis and lipid mobilization. This study is also in agreement with previous studies which had indicated a changing responsiveness to temperature during the annual cycle of the Gulf killfish.

Animals↗
PubMed2002

s-IgA response in females following a single bout of moderate intensity exercise in cold and thermoneutral environments.

Previous research has linked exercise under unfavourable environmental conditions to decreased concentration and/or secretion rate of secretory immunoglobulin A (s-IgA). The purpose of this study was to investigate the influence of moderate exercise in a thermoneutral (TN) and a cold (COLD) environment on the concentration of s-IgA and the secretion rate of s-IgA in moderately active females. Sixteen females (23.4 +/- 6.8 yrs, 61.1 +/- 5.9 kg, 1.64 +/- 0.07 m) served as subjects for this study. On separate occasions, one week apart, all subjects ran or walked for 30 minutes at 71 % of individual heart rate reserve on an outdoor (1 degrees C) or an indoor track (24 degrees C). Unstimulated saliva samples were collected for 4-min immediately pre (PR), post (POST), and 30-min post (30POST) exercise. Profile of Mood State (POMS) questionnaires were completed pre and post exercise intervention and Global Mood State (GMS) was calculated. The absolute concentration of s-IgA, and total non-specific protein were measured and the secretion rate of s-IgA and s-IgA:Protein were calculated. Analysis of Variance (ANOVA) revealed that flow rate increased in COLD and decreased in TN such that it was significantly lower (POST) and (30POST) in the TN environment when compared to COLD. There was a significant increase in the secretion rate of s-IgA at 30POST for the COLD trial and a significant decrease at 30POST for the TN trial. No significant differences were found for the concentration of s-IgA, the s-IgA:Protein:ratio, or GMS. Stepwise regression revealed that with all predictors in the model, only the concentration of s-IgA accounted for a significant proportion of the variance in cold temperature, while in the TN environment, both the concentration of s-IgA and the flow rate accounted for significant proportions of the variance. These findings suggest that moderate exercise in cold temperatures does not decrease secretion rate of s-IgA, while exercise in TN temperatures does.

Adult↗
PubMed1998

Increased heat shock protein expression after stress in Japanese quail.

Heat shock proteins (HSPs) have been shown to provide information on the biological impact of environmental stress to organisms, yet none have investigated the HSP response to stress in birds. Japanese quail were exposed to seven different stressors (mild restraint, loud noise, inescapable irritation, cold temperature, isolation in darkness, and two stressful social situations) and expression of HSP30, 60, 70, and 90 in heart, liver, lung, kidney and gonads was examined. Tonic Immobility (TI) tests were also conducted to assess whether the stressors increased fear response. Increased expression of HSP70 was found in the myocardial tissue of birds exposed to loud noise, inescapable irritation, cold temperature, and isolation in darkness. Increased expression of other HSPs was not apparent in the heart or any of the other all tissues examined. Longer TI was observed only in birds exposed to the noise stress. Evidence is presented that a fairly wide range of stressors caused increased expression of HSP70 in the Japanese quail myocardial tissue and that HSPs may provide useful biomarkers for the study of environmental stress in birds.

Acoustic Stimulation↗
PubMed1996

Warming lignocaine reduces the pain of injection during local anaesthetic eyelid surgery.

The injection of local anaesthetic solutions is frequently a painful and unpleasant experience for patients. A double-masked randomised controlled trial was performed to study the potential benefit of warming lignocaine during local anaesthetic minor surgical procedures on the eyelids. The pain of subcutaneous injection of 1.5 ml of 2% lignocaine at room temperature (cold) and body temperature (warm) was compared in 60 patients during the surgical incision of solitary meibomian cysts of one eyelid. Patients were randomly allocated to receive either warm or cold lignocaine. Pain was assessed subjectively by the use of a linear analogue pain scale ranging from 0 to 100. The median pain score for the group receiving cold anaesthetic (19.5) was found to be greater than that for the warm group (10.0; p = 0.02). In conclusion, the simple process of warming lignocaine to 37 degrees C was found to reduce the pain associated with its injection significantly. It is recommended that this technique be more widely adopted in order to minimise patients' discomfort.

Adolescent↗